Monophase, short travel, electromagnetic actuator having a good electric power/force ratio

ABSTRACT

A monophase electromagnetic actuator including at least a ferromagnetic part integral with a member movable along a direction Y, a fixed stator part made of soft magnetic material and including at least on electrical coil, and a thin transversely magnetized permanent magnet. The fixed stator part and the ferromagnetic part define between each other at least two air gaps arranged symmetrically with respect to the medial plane perpendicular to the axis of displacement of the movable member and passing through the middle of the permanent magnet. The length of the ferromagnetic part is approximately equal to the length of the permanent magnet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a single-phase electromagnetic actuator,designed more particularly for applications requiring low-amplitudestrokes.

2. Discussion of the Art

Actuators are known in the state of the art that include a first partmoving along a direction Y and a second, fixed stator part made of amaterial with a very high magnetic permeability that contains at leastone coil. Such actuators are, for example, claimed in the applicant'sFrench Patent No. 2,648,633. The actuator, according to this embodiment,includes a transversely magnetized thin magnet with the peculiarity ofproviding a constant force throughout the entire stroke and an absenceof magnetostatic force.

Also known from the prior art are actuators described, for example, inEuropean Patent No. 157,632 or U.S. Pat. No. 4,779,582. These actuatorscontain two electrical coils acting antagonistically on a movable unitcontaining a thick-walled permanent magnet.

Such devices of the prior art present the disadvantages of the law ofnonlinear force in relation to the current injected into the coils, alarge amount of occupied space in the radial direction and a lowefficiency in force per watt.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an actuator optimizedfor short strokes and to provide an actuator that presents a high levelof force per watt.

To this end, the actuator according to the invention has a fixed statorpart and a movable ferromagnetic part defining between them two gapsarranged symmetrically with respect to the median plane perpendicular tothe movement axis Y of the radially magnetized movable unit which passesthrough the middle of a permanent magnet, with the length of the movableferromagnetic part approximately equal to the length of the permanentmagnet. The radial gap between the fixed magnet and the ferromagneticpart is made as short as mechanically possible.

When the movable ferromagnetic part is in a median position with respectto the magnet and to the fixed stator part, the magnetic flux due to themagnet is shared equally between both gaps in the absence of a currentin the excitation coil.

When current circulates through the excitation coil, it creates fluxthat is added to or subtracted from that of the permanent magnet.According to the direction of the flux generated by the coil, it willclose preferentially in one or the other of the gaps, which causes themovable ferromagnetic part to move in the direction of the gap crossedby the addition of the two fluxes.

This type of actuator presents the particularity of producing a largemagnetostatic force in each one of the two stable positions withoutcurrent at the end of the stroke. In order to reduce the proportion ofmagnetostatic force in relation to the force due to the current, thegaps may be advantageously tilted with respect to axis Y by an angle onthe order of 45°.

According to a preferred variation, the fixed stator part consists of anexternal cylindrical tube made of a soft magnetic material, which isclosed at each end by a flange made of the same material with a conicalsurface. Advantageously, the coil is housed in the external cylinder andthe fixed magnet is housed within the internal diameter of the coil; itpreferably consists of a high-energy, radially oriented magnet such asthose offered by the company DAIDO STEEL Ltd. The movable magnetic partconsists of a tubular part made of a soft magnetic material with aconical surface at each end which complements that of the fixed statorpart.

Advantageously, the coil is housed in a cylindrical cavity provided inthe fixed stator part.

According to one variation, the actuator has two annular coils arrangedsymmetrically with respect to the median crosswise plane, housed incylindrical cavities provided in the fixed stator part. This embodimentmakes it possible to use the actuator bidirectionally in single-polecontrol and makes it possible to insert a soft magnetic material betweenthe two coils to facilitate closing the magnetic flux between the magnetand the external cylinder, rather than through the thickness of thecoil's copper.

According to one preferred embodiment, the actuator has two springsexerting at each end of the movable unit a repelling force orientedalong the Y axis and designed to compensate for the naturalmagnetostatic force of this structure. Thanks to this method, aapproximately constant force over the entire stroke of the actuator isachieved.

According to one particular variation, the actuator has a second movableferromagnetic part coaxial with the first movable ferromagnetic part.This embodiment makes it possible to arrange both movable units inopposite directions.

Preferably, the magnet is fixed and, according to a particularvariation, the radially oriented cylindrical magnet is replaced by 3tiles that form sections of approximately 120°, or by a series of thinrectangular magnets distributed regularly on a diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reading the followingdescription which makes reference to the attached drawings in which:

FIG. 1 presents a cross section in 2:1 scale of an actuator according tothe invention,

FIG. 2 presents a lengthwise cross section of an embodiment variation;

FIG. 3 presents a cross section through plane AA of this variant;

FIG. 4 presents a view of an actuator according to a second variant;

FIG. 5 presents a view of an actuator according to a third variant;

FIG. 6 presents a view of an actuator according to a fourth variant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The actuator represented by way of a nonlimiting example in FIG. 1contains a fixed stator part consisting of two cylindrical parts (1, 2)joined by a tubular closing piece (3), with all three coaxial parts madeof a soft magnetic material.

The cylindrical parts (1, 2) present a front part respectively (4, 5) inan annular shape and an internal part respectively (6, 7) presenting aconical surface (8, 9). The length of the closing piece (3) is 37 mm, inthe described embodiment example, and the external diameter of the fixedstator part is 45 mm.

The movable ferromagnetic part (10) is created by a tubular part made ofa soft magnetic material presenting at its two front ends (11, 12)conical surfaces defining with the conical surfaces (8, 9) of the fixedstator part two annular gaps (13, 14). The width of the gap, measured inthe Y direction of movement of the movable ferromagnetic part, is 1 mm.

The actuator contains an annular coil (15) consisting of a winding ofcopper wire. This coil (15) is housed in a cylindrical cavity of thefixed stator part and, when current flows through in the aforementionedcoil, causes the conduction of magnetic flux conducted by the closurepart (3), the first gap (13), the movable stator part (10), and thesecond gap (14).

The permanent magnet (16) consists of a radially magnetized tubularpart. It is fastened to an insulation part (17) which seals the cavityin which the electric coil (15) is housed. This insulation part is madeof plastic.

The movable ferromagnetic part (10) is an integral part of a movableunit (18) with a tubular shape for coupling with an external means, forexample, the tip of a valve, or, in the embodiment represented in FIG.4, a high-frequency contact blade.

The movable unit (18) is taken to the median rest position by twosprings (19, 20) acting on shoulders respectively (21, 22) providedinside the movable unit (18). The movable unit (18) has vents (23through 26) to prevent the compression of air inside the gaps (13, 14).

By way of an example, an actuator according to this embodiment developsa force of 40 N with an electrical power of 6 W and for a movement of ±1mm in relation to the median plane of symmetry (27).

FIGS. 2 and 3 represent cross sections of an embodiment variation whichimplements two tubular, coaxial movable stator parts (40, 41), movableaxially between the two front parts (1, 2) of the fixed stator partwhich defines the gaps (44 through 47).

Balls (48) are positioned in tubular housings provided in the permanentmagnet (16). These balls (48) position and guide the movable statorparts (40, 41).

The flow of current through the annular coil (15) causes movement inopposite directions of the two movable stator parts (40, 41).

FIG. 4 represents a variation of the actuator presenting the generalcharacteristics of the actuator shown in FIG. 1, the movable unit ofwhich drives a cylindrical coupling rod (50). In the embodiment shown,there are no return springs in order to use the magnetostatic force ateach end of the stroke, resulting in two stable positions in the absenceof current.

FIG. 5 shows an embodiment variation in which the permanent magnetconsists of an assembly of three thin tile-shaped magnets (51, 52, 53)forming sections of approximately 120°.

In the embodiment shown in FIG. 6, the permanent magnet consists of sixparallelepipedal magnets (54 through 59) spaced at regular angularintervals.

The invention is described in the foregoing by way of nonlimitingexamples. It is well understood that a person skilled in the art wouldbe able to realize different variations without thereby going beyond theframework of the invention.

We claim:
 1. A single-phase electromagnetic actuator comprising:a firstmoveable unit which is movable along an axis of movement and arrangedsynmetrically with respect to a median plane perpendicular to said axisof movement, said first movable unit integrally comprising at least oneferromagnetic part: a fixed stator part formed from a soft magneticmaterial and defining at least two gaps with respect to said at leastone ferromagnetic part, said at least two gaps being arrangedsymmetrically with respect to said median plane; an electrical coilhoused in at least one cavity disposed within said fixed stator part; atransversely magnetized thin permanent magnet arranged such that saidmedian plane intersects a middle of said thin permanent magnet, saidmagnet comprising a thin radially magnetized tubular part located in thecavity in which the electrical coil is housed and inside an internaldiameter of the electrical coil, wherein a direction of motion of saidfirst movable unit corresponds to a direction of current flowing throughsaid electrical coil, and wherein an amount of motion of said firstmovable unit corresponds to an amount of said current; and two springs,each of said springs exerting a repelling force upon a selected one offirst and second ends of the first movable unit, said repelling forcebeing oriented along the axis of movement.
 2. A single-phaseelectromagnetic actuator comprising:a first moveable unit which ismovable along an axis of movement and arranged symmetrically withrespect to a median plane perpendicular to said axis of movement, saidfirst movable unit integrally comprising at least one ferromagneticpart; a fixed stator part formed from a soft magnetic material anddefining at least two gaps with respect to said at least oneferromagnetic part, said at least two gaps being arranged symmetricallywith respect to said median plane, wherein said at least two gaps eachform an angle with the axis of movement, said angle being between 0° and90°; an electrical coil housed in at least one cavity disposed withinsaid fixed stator part; and a transversely magnetized thin permanentmagnet arranged such that said median plane intersects a middle of saidthin permanent magnet, said magnet comprising a thin radially magnetizedtubular part located in the cavity in which the electrical coil ishoused and inside an internal diameter of the electrical coil, wherein adirection of motion of said first movable unit corresponds to adirection of current flowing through said electrical coil, and whereinan amount of motion of said first movable unit corresponds to an amountof said current, and wherein:the fixed stator part comprises twocylindrical parts formed from a soft magnetic material and joined by atubular closure part, each of said two cylindrical parts having anannular front part extended by a center part with a conical surface; thefirst movable unit comprises a first movable tubular part formed from asoft magnetic material and having first and second ends, each of saidfirst and second ends having a conical surface that complements aconical surface of the fixed stator part; and the thin tubular part ofsaid thin permanent magnet is radially magnetized.
 3. A single-phaseelectromagnetic actuator comprising:a first moveable unit which ismovable along an axis of movement and arranged symmetrically withrespect to a median plane perpendicular to said axis of movement, saidfirst movable unit integrally comprising at least one ferromagneticpart; a fixed stator part formed from a soft magnetic material anddefining at least two gaps with respect to said at least oneferromagnetic part, said at least two gaps being arranged symmetricallywith respect to said median plane, wherein said at least two gaps eachform an angle with the axis of movement, said angle being between 0° and90°; an electrical coil housed in at least one cavity disposed withinsaid fixed stator part; a transversely magnetized thin permanent magnetarranged such that said median plane intersects a middle of said thinpermanent magnet, said magnet comprising a thin radially magnetizedtubular part located in the cavity in which the electrical coil ishoused and inside an internal diameter of the electrical coil, wherein adirection of motion of said first movable unit corresponds to adirection of current flowing through said electrical coil, and whereinan amount of motion of said first movable unit corresponds to an amountof said current; and two springs, each of said springs exerting arepelling force upon a selected one of first and second ends of thefirst movable unit, said repelling force being oriented along the axisof movement.
 4. A single-phase electromagnetic actuator comprising:afirst moveable unit which is movable along an axis of movement andarranged symmetricall with respect to a median plane perpendicular tosaid axis of movement, said first movable unit integrally comprising atleast one ferromagnetic part; a fixed stator part formed from a softmagnetic material and defining at least two gaps with respect to said atleast one ferromagnetic part, said at least two gaps being arrangedsymmetrically with respect to said median plane; an electrical coilhoused in at least one cavity disposed within said fixed stator part;and a transversely magnetized thin permanent magnet arranged such thatsaid median plane intersects a middle of said thin permanent magnet,said magnet comprising a thin radially magnetized tubular part locatedin the cavity in which the electrical coil is housed and inside aninternal diameter of the electrical coil, wherein a direction of motionof said first movable unit corresponds to a direction of current flowingthrough said electrical coil, wherein an amount of motion of said firstmovable unit corresponds to an amount of said current, and wherein:thefixed stator part comprises two cylindrical parts formed from a softmagnetic material and joined by a tubular closure part, each of said twocylindrical parts having an annular front part extended by a center partwith a conical surface; the first movable unit comprises a first movabletubular part formed from a soft magnetic material and having first andsecond ends, each of said first and second ends having a conical surfacethat complements a conical surface of the fixed stator part; and thethin tubular part of said thin permanent magnet is radially magnetized.5. A single-phase electromagnetic actuator according to claim 4, furthercomprising two springs, each of said springs exerting a repelling forceupon a selected one of first and second ends of the first movable unit,said repelling force being oriented along the axis of movement.
 6. Asingle-phase electromagnetic actuator according to claim 4, wherein saidelectrical coil is symmetrically arranged in relation to the medianplane and housed in at least one cylindrical cavity within the fixedstator part.
 7. A single-phase electromagnetic actuator according toclaim 6, further comprising two springs, each of said springs exerting arepelling force upon a selected one of first and second ends of thefirst movable unit, said repelling force being oriented along the axisof movement.
 8. A single-phase electromagnetic actuator according toclaim 4, wherein said electrical coil is housed in at least onecylindrical cavity within the fixed stator part.
 9. A single-phaseelectromagnetic actuator according to claim 8, wherein said electricalcoil is symmetrically arranged in relation to the median plane.
 10. Asingle-phase electromagnetic actuator according to claim 8, furthercomprising two springs, each of said springs exerting a repelling forceupon a selected one of first and second ends of the first movable unit,said repelling force being oriented along the axis of movement.